Ni^II COMPLEXES : MAGNETISM CAN LEAD TO WRONG ASSIGNMENT OF TETRACOORDINATED GEOMETRY. Hartmut Wunderlich, Institut für Anorganische Chemie und Strukturchemie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany

Tetracoordinated Ni^II complexes reveal frequently planar arrangement of the core, but several crystal structures with tetrahedral or intermediate geometry (dihedral angle at Ni^II between 0deg. and 90deg.) are also reported. By measurement of the magnetic moment the geometry has been assigned corresponding to the relation: paramagnetism (u_eff =3-4 B.M.) - tetrahedral, diamagnetism - planar. This rule is violated by the compounds 1 and 3a which are paramagnetic and yet planar complexes. The dependence of the coordination geometry on the type of residues R¹ and R² is revealed by a series of crystal structure determinations.

R² X compd. u_eff[BM] dih. angle [¡]

P Ni/2 1 3.4 0

R² N 2 3.0 82.4

R¹ 3a 3.3 0

3b 3.3 86.2

R¹ ; R² X = O X = S 4 3.3 81.6

i-Pr ; t-Bu 1^[1] 2 5 diam. 4.5

c-Hex ; t-Bu 3a,3b^[2] 4^[3] 6 3.1 41.7

-CH₂-CH₂- ; t-Bu 5 7 3.3 68.8

-CH₂-CMe₂- ; Et 6

Et ; t-Bu 7

compd.:             2             5             6             7   
 a [pm]       1612.3(2)     1337.4(8)       877.4(1)    1730.4(4)     
b [pm]        1168.4(2)     1619.7(8)     1233.5(2)     1305.5(3)     
c [pm]        1581.5(2)     1281.4(6)     2133.9(3)     1944.4(4)     
[[beta]]        90.74(2)    109.20(4)       92.33(1)    105.80(2)     
[deg.]                                                                
sp.group; Z     P21/c; 4      P21/c; 4      P21/c; 4      P21/n; 4    

[1] Angew. Chem. Int. Ed. Engl. 31, 612-613 (1992).

[2] ibid. 32, 907-909 (1993).

[3] Z. anorg. allg. Chem. 606, 119-132 (1991)